1. Field of the Invention
Apparatus and methods consistent with the present invention relate to searching channels, and more particularly, to updating data regarding effective channels by automatically detecting whether stored digital channels are scrambled according to a user command and a method for searching channels thereof.
2. Description of the Related Art
Recently, as digital broadcasting, i.e., digital cable broadcasting, digital satellite broadcasting and digital terrestrial wave broadcasting, has developed, the number of viewable channels has surpassed 100 and continues to increase.
In contrast to public broadcasting, viewers must pay television subscription fees to digital broadcast providers to view desired channels, and digital broadcast providers produce a high quality of broadcast programs using the fees. To protect such broadcast programs and view rights of subscribers, the digital broadcast providers utilize a conditional access system (CAS) so that only subscribers may view the programs.
Using the CAS, digital broadcast providers scramble and transmit broadcast signals according to their own encryption system, and only subscribers can descramble the broadcast signals to view the broadcast program. Broadcast signals are scrambled by introducing particular signals into the broadcast signals or disordering the scan lines, resulting in abnormal images. Such scrambling can be decoded using a decoder dedicated to scrambling. In the United States, scrambling is decoded by inserting a cable card.
In general, viewers wish to view only a few channels among the large number provided, and thus subscribe to only a few digital broadcast services. Accordingly, there are fewer channels viewable to viewers than non-viewable scrambled channels, and as digital broadcast providers and channels increase, viewers find a greater proportion of scrambled channels. As a result, if a user searches for channels to view digital broadcasting, more scrambled channels are searched than viewable channels, resulting in user inconvenience such as increased searching time.
Therefore, modern televisions not using a cable card are configured to determine whether a channel is a scrambled channel when automatically setting channels, and to delete a channel if it is a scrambled channel. However, scrambled channels are deleted while automatically setting channels, so the user does not realize even there are scrambled channels. Additionally, as digital broadcast providers scramble and descramble a channel, automatic channel setting is carried out again in order to delete channels which have changed from a descrambled state to a scrambled state, and to recover channels which were deleted while automatically setting channels if they have changed to a descrambled state. If the automatic channel setting is carried out again, all of the physical transmission channels (PTCs) have to be tuned to search channels having a broadcast signal and detect whether the channels are scrambled. Consequently, this takes a considerable length of time.